1. Field of the Invention
The present invention relates to systems and methods for preempting traffic signals. More particularly, the present invention relates to systems and methods allowing emergency and other vehicles to control or preempt traffic signals.
2. Present State of the Art
Cities and communities are in a continual state of change. Some communities are experiencing tremendous growth, while others are attempting to attract new businesses. Additionally, each city or community is faced with a variety of problems including the problem of developing an adequate transportation system.
The scope of the transportation system is quite broad and includes topics from road construction to mass transit. One primary concern of the transportation system is the road or street system, which must be capable of handling the traffic of a community. Practically all drivers are aware of the delays caused by rush hour, construction, and signal lights. These delays can cause many problems for everyone, especially emergency vehicles.
In addition to the delays, there are different types of roads which have distinct purposes. Main roads are designed to handle large volumes of traffic, while roads built in the suburbs and residential neighborhoods, on the other hand, are different in that they are designed for slow careful driving. In short, the roads of a community are built with a variety of different concerns and purposes in mind.
Regardless of how the roads are built, the traffic on those roads must be controlled, and one method of controlling the traffic on the roads and streets of a community is to use signal lights. Many signal lights are designed with a timing mechanism. With timed signal lights, vehicles wait a certain amount of time before they are presented with a green light, at which point they proceed through an intersection. At intersections with timed signal lights, it is possible for a vehicle to be the only vehicle at the intersection, yet the vehicle must wait for the timer to expire before the signal light presents them with a green light
Today, many signal lights are being replaced or upgraded and have the ability to sense the presence of a vehicle. The advantage of these signal lights is that they can respond to actual traffic conditions. For example, at a signal light with a turn signal, the traffic light can sense when there are no more vehicles turning. When this condition is sensed, the turn signal is deactivated while other lights are activated so that other vehicles, which were waiting to enter the intersection, may proceed.
While these signal lights have improved the control and the flow of traffic, they cannot respond effectively to emergency vehicles which may need to cross or enter the intersection immediately. As a result, an emergency and other vehicles may be delayed behind traffic while waiting for the light to change.
There are many instances where it is imperative that an emergency vehicle proceed through an intersection quickly. In many accidents, time is critical and an ambulance that has green lights at intersections will be able to arrive much quicker. Police cars involved in high speed chases can prevent potentially fatal injuries by controlling the intersections through which the chase is occurring. Police cars will also be able to arrive at crime scenes faster. If the lights of an intersection are controlled or preempted, persons not hearing the sirens of an emergency vehicle are prevented from entering the intersection being preempted. In short, the public can greatly benefit by permitting emergency or other approved vehicles to control or preempt signal lights.
Several attempts have been made to address this issue. One method includes the use of optical devices to transmit the message that a vehicle is requesting a light change or preemption. This method requires that an optical device be mounted on each signal mast for each direction. This can be quite expensive and requires that the optical device and the corresponding emergency vehicle be able to see each other. Other systems employ the use of global positioning technology. This method has significant drawbacks, even though it may be effective. For instance, the system requires extensive programming, not only for the emergency vehicles, but also for the location of each intersection. Also, the position of the vehicle must constantly be reevaluated. Other methods require that a highly directional transmit or receive antenna be mounted for each direction of travel in addition to the transmit antenna in the vehicle.